Spermicides come in the form of vaginal creams, films, gels, suppositories, sponges and tablets, working both as a barrier that prevents sperm from entering the cervical os (the external orifice of the uterus), and by reducing the sperm’s motility. 

Because spermicides are only 71-85% effective against pregnancy, it is usually advised as a back-up contraceptive that can be used concurrently with another method, such as a diaphragm or a condom. 

Spermicides can increase sexual pleasure by providing additional security against pregnancy, as well as increasing vaginal lubrication. 

However, it may have an unpleasant taste if used during oral-genital sex and it can irritate the genitalia of the man or woman. As mentioned above, spermicides do not protect against STI and may actually increase the risk of transmission if they cause irritation.